Eddy current inspection is a commonly used technique for detecting discontinuities or flaws in the surface of components of a gas turbine engine. Eddy current techniques are based on the principle of electromagnetic induction in which eddy currents are induced within the component under inspection. The eddy currents are induced in the component by alternating magnetic fields created in a coil of an eddy current probe, referred to as a drive coil, when the probe is moved into proximity with the component under inspection. Changes in the flow of eddy currents are caused by the presence of a discontinuity or a crack in the test specimen. The altered eddy currents produce a secondary magnetic field which is received by the eddy current probe coil or a separate sense coil in the eddy current probe which converts the altered secondary magnetic field to an electrical signal which may be recorded on a strip chart or similar device for analysis. An eddy current machine operator may then detect and size flaws by monitoring and analyzing the recorded signals. Flaws or defects are detected if the electrical signal exceeds a predetermined voltage threshold.
One problem with inspecting components is that the components can contain closed surfaces, such as round or shaped holes, which have heretofore required approximately six hours of labor time per part to inspect for flaws and/or defects. State of the art single coil inspection mode, depending on the area to be inspected, can require as many as thirty passes through the same hole for adequate inspection, taking as long as 4 minutes per area.
It would be desirable, then, to be able to provide capability for the rapid inspection of closed surfaces, such as round or shaped holes, using an inspection device which includes an eddy current array circuit, which is not subject to the foregoing disadvantages. The objects, features and advantages of the present invention will become more readily apparent in the following description when taken in conjunction with the appended drawings.